Engine misfire may be determined via monitoring an engine crankshaft position sensor. Changes in engine speed and acceleration during an engine rotation may be indicative of the presence or absence of engine misfire. Engine misfire may be characterized as an air-fuel mixture in a cylinder that fails to ignite during a cycle of the cylinder. Engine misfire reduces engine torque, increases engine emissions, and may degrade engine components, such as the catalyst converter. Therefore, it may be desirable to determine if misfire is present and take mitigating actions to reduce the possibility of misfire during future combustion events.
An engine controller may process an engine crankshaft position sensor signal to provide an associated crankshaft speed or acceleration. The crankshaft speed or acceleration may be monitored during a power stroke of a cylinder being monitored for misfire to judge whether or not misfire has occurred in the cylinder being monitored. For better separation of misfiring and normal firing events, the crankshaft speed and acceleration are typically filtered and re-scaled to misfire index values (these index values could be normalized or not normalized) in order to achieve better separations between normal firing and misfiring events. A misfire threshold is the criteria for separating misfire index values into normal firing or misfiring cylinder events. Most manufacturers adopt after-processing methods to develop misfire thresholds. Such methods rely on the post processing of the test data collected from development vehicles to determine the misfire thresholds. Such misfire thresholds cannot fit the need to address vehicle-to-vehicle variance, vehicle life-cycle changes, and new engine control strategies that will significantly change the noise level of misfire index values in the same speed-load zone.
The inventor herein has recognized the above-mentioned limitations and has developed an engine control and signal-processing method, comprising: dividing an engine operating region into a plurality of zones for misfire threshold determination, each zone within the plurality of zones defined by an engine speed range and an engine load or engine torque range; the misfire threshold for each zone is determined by two sets of statistical parameters (the statistical parameters include but are not limited to mean value, standard deviation, maximum, and minimum values for normal firing and misfiring events respectively): zone-level parameters and buffer-level parameters; zone-level parameters stored in memory representing each of the plurality of zones are slowly updated to catch the vehicle life-cycle changes on misfire index values; buffer-level parameters are real-time calculated from the circular buffer of the immediate past misfire index values to quickly adapt to the engine operation conditions on real-time misfire index values; and dynamically output the misfire threshold by combining zone-level and buffer-level parameters and mixing the associated statistical parameters; and adjusting an actuator via a controller responsive to an indication of misfire based on the misfire threshold level.
By including individual misfire threshold levels for each engine operating zone, it may be possible to provide the technical result of improving engine misfire detection. Individual misfire threshold levels in each engine operating zone may be dynamically tailored to engine operating conditions so that indications of actual engine misfire may be clearly distinguished from non-misfire conditions. For example, standard deviation, mean value, maximum, and minimum of misfire index values for normal combustion events may be real-time assessed to verify if a current misfire threshold level is too high or too low to cause false detections. Likewise, standard deviation, mean value, maximum, and minimum of for misfire index values for misfire events may be real-time assessed to verify if the current misfire threshold level is too high or too low to trigger false detections. The misfire threshold level may be determined based on statistics for the normal combustion event misfire index values and the misfire event misfire index values. Consequently, misfire thresholds for an engine operating zone may be based on misfire index values that occur within an engine operating zone rather than misfire index values that occur outside of the engine operating zone. As a result, misfire threshold values in an engine operating zone may be more closely tailored to conditions within the engine operating zone, thereby improving threshold values and misfire detection.
The present description may provide several advantages. Specifically, the approach may provide improved misfire detection so that fewer false positives are indicated. In addition, the approach may adjust engine operation to reduce negative impacts caused by misfires based on improved misfire detection. As such, engine emissions and fuel economy may be improved.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.